CIPS Calibration Review Aimee Merkel Bill McClintock

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CIPS Calibration ReviewAimee MerkelBill
McClintock
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CIPS Science Measurement Requirements
CDR Science Requirements Document Summary
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CIPS Ground Calibration Summary

• Calibration Activities
• Unit level tests (detector components, assembled
  detector units, filters, lens systems)
• Camera level tests
• Preenvironmental instrument calibrations
• Environmental test
• Postenvironmental instrument calibrations
• Post spacecraft IT calibrations
• Instrument Calibrations
• CCD characterization (read noise, dark current )
• TDI (Time Delayed Integration Nadir Cameras
  only)
• Wavelength Range
• Flat Field
• Field of View
• Linearity
• Distortion
• Polarization
• Off-axis response (Stray and scattered light
  performance)

• Point Spread Function
• Absolute sensitivity
• Focus
• Out of band rejection
• Light leaks
• Camera to camera alignment
• Camera to reference optical surface (ROS)

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Calibration Measurement Summary
Requirement
Measurement
Cameras meet or exceed all performance
requirements
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Raw Image to Calibrated Image
Process of converting raw image in data numbers
(DN) to calibrated image (Level 1A data product)
in units of Gary. (1 Gary 1 x 10-6 Albedo)
Subtract stray light Stray (i,j)
Correct for non-linearity Nlin
Raw Image DN(i,j)
Subtract Dark Dark (i,j)
Place holder (no evidence of Stray light issues)
Account for Sensitivity of Camera. Rinst(I,j,?,T,
HV)Fsun
Divide out Flat Field FF
Account for integration Period ?t
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Dark Image Dependence on CCD Temperature

• Offset (set by electronics)
• Electrical offset added to image to provide a
  baseline signal to avoid negative readout.
• Applied after analog amplifier but before
  digitization. Has no non-linearity issues.
• Dark Current
• Thermal noise that accumulates with image read
  out time (accumulates over rows).

• High Quality CCDs!
• Typical characteristics
• Offset 90DN
• Dark Current 0.1 DN/sec or 3.2
  e/sec

Electrical Offset and Dark Current vary
differently with temperature.
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CIPS CCD Temperature Ranges
CCD Temp only varies by 1ºC over orbit
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Dark Image Dependence on CCD Temperature
Interpolated over orbit Temperature
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Linearity (N)
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Camera Flat Field
Integrating Sphere used to uniformly illuminate
Camera FOV

• Variation from Pixel to Pixel due to
• Photocathode variation
• Lens System Cos4?

• Flat Field Requirement 1 Accuracy
• Measured
• Relative sensitivity across the 44º FOV 1 or
  better
• Repeatability of Flat images to 0.1

• In-flight Image Calibration
• Divide out normalized Flat Field from each image

Normalized Flat Field Percentage of Max Signal
Camera 0 Flat Field
Pixel
Pixel
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Radiometric Sensitivity of Camera
R(i,j) in units of DN/sec/Gary
Still need to account for sensitivity dependence
on Temperature (T) and High Voltage(HV)
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Correct Camera Sensitivity for T and HV
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Calibrated Image
Calibrated Image (Albedo)
Raw Image Data Number DN
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Calibrated Image
Calibrated Image in Units of Garys Level 1A data
product
Processing test up to Level 1A data product
successful. Ready for Launch!!!
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Post Launch CIPS Calibration Overview

• In-Flight Calibration Task List
• Absolute pointing knowledge established by
  viewing UV stars (0.2 knowledge requirement)
• Detector characterization
• Dark field
• Intensifier characterization
• Camera to camera alignment (science images)
• Absolute sensitivity by viewing UV stars.
• Flat Field images and Relative sensitivity over
  the FOV (clear field images)
• Stray and scattered light performance (shadow
  images)
• Light leaks (shutter test)

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Extra Slides
EXTRA SLIDES
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CCD Acceptance Test

• Each flight CCD went through extensive acceptance
  testing with the flight electronics.
• At 3 different temperatures (25ºC, -10ºC, -40ºC)
  analyzed dark field
• Number of Hot Pixels
• Read Noise
• Number of electrons introduced (noise) when
  reading out of device.
• Effects all pixel values uniformly.
• Dark Current
• Thermal noise that accumulates with image
  read out time.
• CIPS CCD has a 17 sec readout time, the dark
  current accumulates over rows.
• For example First row read out has less
  dark current than the last row read out.
• Reported as electrons/second
• Offset (set by electronics)
• Signal readout from CCD when not exposed to
  light.
• Accommodates temporal shifts in electronics,
  temperature stability and read noise.
• Avoids negative readout.
• Photon Transfer
• Checks the full well, offset, gain, linearity of
  the CCD.

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CCD Acceptance Test

• Each CCD is 2048 X 2048 pixels. Only
• 1360 x 1360 pixels are used.
• Dark images are used to characterize the CCDs.

CCD 01 in Camera 0

• High Quality CCDs!
• Typical characteristics
• Hot Pixels lt 0.07
• Read Noise 38 Electrons
• Offset 90DN
• Dark Current 0.1 DN/sec or 3.2
  e/sec

Integration Period (s)
IT calibration Built up instrument
Read Noise 45 Electrons
Data Number (DN)
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Camera Field of View

• Field of View
• 44º square for all cameras
• Requirement
• Minimum of 44º square

44º 1426 Pixels
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Linearity
Linearity measured using the integrating
sphere. Integration period incremented until
saturation achieved.

• Camera Linearity
• Linear 3x103 DN
• Completely nonlinear by 104 DN
• Requirement
• Measure linearity to 95 full well

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Camera Distortion
Camera Distortion Measure Took image of grid in
clean room Positioned 10 feet away to fill the
44º FOV Looked at linearity of lines across
FOV Requirement Measure to 1 over the field
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Camera Polarization

• Linear polarization
• Measured both Perp and Para response using a star
  source and Glan-Taylor linear polarizer.
• Response measured at 21 discrete points on the
  detector as displayed below.

• Polarization
• Max 3 in Corners
• Accuracy 1
• Polarization effects are negligible
• Requirement
• Less than 10
• 5 Accuracy

Percent Polarization
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Camera Composite
MY
SUN
MX
PX
PY
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UV Bandpass
Ultraviolet Bandpass 265nm 10nm In-band
Transmission 30
Measured Filter
Transmission
Wavelength (nm)
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Near Field Off Axis Response
Near Field Off Axis Response Declines 103 in 2
Degrees
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Radiometric Calibration
Radiometric sensitivity is measured using a
NIST-traceable 1-KW quartz-halogen standard lamp
and a reflectance screen
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Radiometric Calibration
Measurement sequence repeated 20 Times at 4 high
voltages
Signal exponential function of HV SNR varies by
10 for HVgt 700 volts